The only lanthanide with no stable isotope — it decayed away and had to be made in a reactor.
- Atomic number
- 61
- Atomic mass
- [145] u
- Phase
- Solid
- Electron configuration
- [Xe] 4f⁵ 6s²
- Melting point
- 1,315 K · 1,041.9 °C
- Boiling point
- 3,273 K · 2,999.9 °C
- Density
- 7.26 g/cm³
- Electronegativity
- 1.13
- Period / Group
- 6 / —
- Discovery year
- 1945